Gas tube controlled servo system



' June 14, 1949. I

w. c. GRABAU 2,473,424 us was conTRbnL-En'smvo srswnu Original Filed July 9, 1942 4 2 Sheets-Sheet 1 HAND CO\NTROL INVENTOR. F|G WILLIAM CHRISTIAN GRABAU June 14, 1949. w. c. GRABAU 2,473,424

GAS TUBE CONTROLLED SERVO SYSTEM Original Fil'ed July 9, 1942 2 Sheets-Sheet 2 OF TOOL }F0R OPERATION Z 62 g POSITION 0F MOTOR CONTROLLED BY TOOL FIG. 3

INVENTOR. WILLIAM CHRISTIAN GRABAU Patented June 14, 1949 GAS TUBE CONTROLLED SERVO SYSTEM William C. Grabau, Brighton, Mass., assignor, by

mesne cuts, to Submarine Signal Company, Boston, Mass., a corporation of Delaware Original application July 9, 1942, Serial No. 450,329. Divided and this application December 9, 1943, Serial No. 513,608

2 Claims. (Cl. 318-30) The present application is a division of application Serial No. 450,329, filed July 9, 1942, now Patent No. 2,352,626.

The present invention relates to a training control system for rotating and directing a rotatable element at varying speeds and to varying positions. The system is more particularly applicable to the control .with the use of an alternating current source and may be applied for training searchlights, radio locators, signaling device and guns.

One advantage in the present system is that great accuracy is obtained by the elimination of the lag or slack in the system. In the present application the training motor driving the element to be trained follows directly and without delay the training of the hand-controlled element. This, in part, is accomplished by the use of a balanced system in which current flows under normal operating conditions through the driving element in both directions and the operation and drive are obtained by the increase of current flow in one direction over that in the other direction so that there is no necessity and no time delay in the building up of the initial current flow in the circuit. This balancing effect is particularly important in the present application because the control must be able to rotate the training gear in what may be called a forward and a reverse direction.

Further advantage is obtained in the present system because of the rapidity of action between the operating hand control and the circuits controlling the driving machine, as will be more clearly understood from the description in the specfication below. In this respect the present invention incorporates in parts some of the features disclosed and claimed in my copending application, Serial No. 432,982, filed March 2, 1942, Patent No. 2,352,626, dated July 4, 1944.

Further merits and advantages of the present invention will be more clearly understood in connection with the drawings illustrating an embodiment of the invention in which Fig. 1 shows a diagrammatic arrangement of the invention; Fig. 2 illustrates a set of curves applicable to the operation of the circuit of Fig. 1; and Fig. 3 shows a modified application of the invention to a machine tool.

In the drawing, the driving motor I repre- 2 sented at M may drive the training apparatus which may, of course, be a searchlight, radio 10- cator or submarine signaling apparatus. Driven on the same shaft with the motor I. is the selfsynchronous repeater 2 with a stator 2' which is electrically connected with the self-synchronous generator stator 3 in which a voltage is induced by means of the winding 3' whose relative position with respect to stator 3 is controlled by the operating crank I. gized by an alternating current supply 5 in the usual manner. The rotor 5 of the motor 2 is relatively the same element as the rotor 3' so that, when rotor 6 and the hand-operated rotor 3' have the same phase displacement, no voltage will be supplied to the output transformer III of the repeater system. Under this condition the voltage developed by the double rectifier I will be zero and therefore there will be no bias on the grids i3 and I6 from repeater 2 and the generator 2. When there is a displacement between 6 and 2', a voltage is developed in the winding II, and therefore the transformer is energized so that a voltage exists across both secondaries II and I2, in which case both grids i3 and ll of the double triode l5 and the grids l6 and ll of the double triode It will become negatively biased. When no bias exists on I 3 and IS, a normal balanced condition prevails in which the driving motor I is at rest. The double triodes l5 and I8, which are preferably of the thermionic type, have their anode-cathode voltage supplied from the alternating current source is which may be the same alternating source as the source 5 through the transformer 20 which has several secondaries 2|, 22, 23, 24 and 25. The secondaries 2| and 25 supply, respectively, the cathode-anode voltages for the tubes I 5 and I8 in a manner that will presently be described. For the tube ii the secondary winding 2| is connected in series with the primary 26 of a transformer 21. This primary winding 26 and the transformer winding 2i are in series with the cathode 28 and the anode 29 of the tube II while the secondary 30 of the transformer 21 is in series with the cathode 3| and the anode 22 of the tube IS. The same arrangement i applied to the tube I8, the transformer 33 operating in the same manner as the transformer 21 with a primary 34 and a secondary 35. the primary 24 being in the series circuit with the cathode 26 and This generator is, of course, eneranode 31 while the secondary 35 is inseries with the cathode 38 and the anode 38. When a normal current is flowing across the tube I between the anode 28 and the cathode 28, the voltage developed across the secondary 2I is partly distributed across the primary 28 of the transformer 21 and across the cathode-anode drop in the tube I5. Since the transformer 21 has approximately a one-to-one ratio, the same voltage is developed between the anode 32 and the cathode 3| as across the primary 26 of the transformer 21.

When the displacementoi the winding 6 of the repeater motor varies with respect to that of the winding 3', avoltage will be generated across the transformer II) which will produce a voltage drop in the resistances 8 and 9 of the rectifier 1, and thereby increase the negative bias on the grids I3 and I4 of the tube I5, and I6 and I1 of the tube I8. since the voltage is applied in opposite phases to the cathode-anode circuits of the tubes I5 and I8, this negative bias will tend to shut off the flow of current in one of the tubes I5 or I8 and therefore decrease the voltage developed across the primary 26 or 34 of the transformer 21 or 33, respectively, applying most of the voltage generated in the secondary winding 2I or 25 across the cathode-anode 28-29 or 36-31. This decrease in voltage in the transformer 21, for instance, will directly decrease the voltage applied between the cathode 3| and the anode 32, and together with the increase in the negative bias on the grid I4 will sharply decrease the cathodeanode current flowing between 3| and 32. The output of this tube flows through a resistancecondenser circuit 40 and 4|, respectively, the resistance of which controls the bias on the gaseous control tube 42. In a similar manner when the displacement between 6 and 3' is in the opposite phase, the control tube 43 has its bias 44 controlled by means of the resistance 45 and condenser 46 connected in shunt in the cathodeanode circuit 38-39 of the tube I8. The grids 41 and 44 of the tubes 42 and 43, respectively, are therefore controlled by the output circuits of the tubes I5 and I8, respectively, according to the. direction of displacement and an increase in grid bias developed by an increase in a voltage output of the rectifier 1 will tend to decrease sharply the bias applied to the grids 41 and 44 of the tubes 42 and 43, respectively, in the manner that has been described in my copending application Serial No. 432,932 mentioned above. The slope of this decaying voltage at one or the other of the grids 41 and 44 becomes steeper with increase of operating displacement voltage. The anode-cathode circuits of the control tubes 42 and 43 are supplied by means of the transformer 48, the secondaries 49 and 50 of which supply respectively the tubes 42 and 43. Whenever the biases on the grids 41 and 44 decrease below the critical value during the positive alternating voltage cycle on the tubes 42 and 43, respectively, the tubes will permit the flow of current and then the circuit is completed through the armature of the motor I and thereby the training gear may be turned in one direction or the other.

' The direction of rotation of the motor I is governed by the relative positions of the rotor 3' of the self-synchronous generator 3 and the rotor 8 of the motor 2. The voltages impressed upon the cathode-anode circuits of the conduction tubes 42 and 43 as well as those impressed on the tubes I5 and I8 are 180 degrees out of phase with each other so that the biases on the grids 41 and will permit conduction only in one of the two conduction tubes. In one relative position of the rotor 3' and the rotor 3, one decaying voltage either on the grid 41 or 44 will be altered by the change of displacement voltage produced in the resistances 8 or 9, in which case the voltage on the selected grid 41 or 44 will cooperate witn the v positive half cycle in one tube, whereas in the other relative position between the rotor 3' and the rotor Ii, the voltage on the other of the grids 41 or 44 will cooperates with the positive voltage on its conduction tube.

This is illustrated in Fig. 2. In this case A may represent the cathode-anode voltage applied across the tube 42 and B the cathode-anode voltage applied across the tube 43. The normal decaying voltage developed on the grids 41 and 44 is in the form shown in curve C or curve D, respectively, when there is no displacement voltage. When there is a displacement voltage in either direction,'then the curve C or D is steepencd and cuts the critical grid voltage curve eariler in the cycle, causing the conduction to fire over a longer period of the cycle. It should be borne in mind that the phases do not change but only their selection and magnitude which are dependent on the relative position of the rotor 6 and rotor 3'.

The potentiometer adjustments 53 and 54 are used to adjust the magnitude of the voltage applied to the grids 41 and 44 as has been explained. These adjustments may be so made that the decaying grid voltage always permits a small amount of current to flow at the end of each positive half cycle as illustrated by the shaded sections s in the figures of curves A and B. This will provide a definite balance when the motor is not moving and has the effect of causing the motor to follow the training gear accurately when the hand control turns the generator rotor 3' in either direction. In the present system the training gear will follow the control even at very slow speeds with an accuracy of less than onehalf a degree displacement between the control and the controlled element.

It will be noted by following through the circuit diagram that the secondary winding 49 is in series with the motor I and the tube 42 so that when the tube 42 fires, current will flow through the motor I in the direction of the arrow 5I. It will also be noted that the winding is in series with the tube 43 and the motor I and that when the grid 44 permits this tube to conduct current, current will flow through the motor I in the direction of the arrow 52.

In Fig. 3 there is shown a special application of the arrangement shown in Fig. 1. In this case the self-synchronous control elements 2 and 3 are replaced by a rotary transformer as is indicated at 60. This is mounted to move as a whole with the movable tool element of the machine up or down according to the double-ended arrow 10. The rotor is provided with a shaft 6| which has a point 64 bearing on the surface 65 of a movable template to whose contour the movement of the tool is to correspond. The surface may be moved in the direction of the arrow 58, in which case the angular position of the rotor 60' will be changed corresponding to the upward and downward motion of the bar 63, the tool following the motion of the point 64 until it has been brought to relatively the same position as the point 84. Under these circumstances when the bar 63 is raised, the displacement of the rotor 50 attached to the shaft 6| from a neutral position 44 simultaneously operating in the same fashion will bring about a movement of the tool and cor- 'respondingly of the whole rotary transformer, tending to return the rotor 60' the same angular displacement to its neutral position where it comes to rest. 2

Since the magnitude of the displacement of the re r with respect to its stator governs the amplitude of the voltage produced, the speed of rotation will be governed bythe displacement between the rotor 60' and its stator. This will be evident from the circuit of Fig. 1. As explained with reference to that figure, the relative displacement of the generator winding 3 with respect to the winding 5 will produce relatively higher voltages developed across the resistances 8 and 9 and this will react to cause'a quicker decay of the voltage in the resistors 40 and 45 and therefore permit conduction earlier in the cycle in one of the tubes erative feature applies to 42 or 43. The same op- Fig. 3 where an increase in displacement, caused by the point 64 or bar 63 being carried higher by the surface of the template 65, will produce a greater displacement voltage in the rotary transformer 50, and therefore, by the action of the rest of the circuit of Fig. 1, a higher speed acting on the tool to restore the elements to their neutral position.

Having now described my invention, I claim: 1. A follow-up system for controlling linear motion of a tool to correspond with the contour of a template comprising a rotary transformer means having rotor and stator elements adapted to produce an electrical voltage corresponding in instantaneous polarity and magnitude to the direction and degree of angular displacement from a neutral position of one of said elements with respect to the other, the displacement of one of said elements being governed by the contour of said template and the displacement of the other by motion of said tool, a motor for moving said tool, gaseous conduction tube means for operating said motor in a forward or reverse direction, said conduction tube means including a pair of gaseous grid controlled rectiflers one for each direction of rotation of said motor and means for applying to the control grid of each rectifier periodic pulse potentials and a direct potential generated by the action of said rotary transformer and corresponding in polarity and magnitude to with respect to the other, the displacement of crating said motor in transformer and one of said elements being governed by the contour of said template and the displacement of the other by motion of said tool, a motor for moving said tool, gaseous conduction tube means for opa forward or reverse direction, said conduction tube means including a pair of alternately activated gaseous grid controlled rectifiers one for each direction of operation of said motor, means for applying to the grid of each rectifier a periodic bias pulse potential synchronized with the respective rectifier alternating anode potential, means for adjusting each of said potential pulses to have a final value just sufficient to produce small equal current flows through each rectifier and thereby in opposite directions through said motor in each cycle of alternating anode potential and means for further applying to said grids a direct control potential generated by the action of said rotary corresponding in polarity and magnitude to the direction and magnitude of said angular displacement.

1 WILLIAM C. GRABAU.

REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS I Gulliksen Jan. 5, 1943 

